In process monitoring and control and in the inspection and quality control of end products in numerous industrial plants, on-line analysis is becoming increasingly important. Within the narrow field of analytical indication, the problems encountered may be overcome for the most part by means of available analytical methods, such as for example titrimetric, photometric, conductometric, or thermometric analysis. Also, the degree of automation of such analytical methods is very highly developed. The basic requirement for all of these analytical methods is the availability of a solution of the sample. This regularly results in difficulties whenever solid samples are to be analyzed. To be sure, it is possible by means specially adapted to particular problems, but otherwise commercially available, to obtain a sample of a larger batch which is thoroughly representative of the composition of the batch. Such samples, however, are only roughly defined in amount. Except in manual methods which are time and labor intensive and consequently expensive, the problem of accurately weighing all or part of a sample, discarding possible residues and quantitatively transferring the weighed sample into a suitable dissolving vessel, has remained largely unsolved.
There has been no lack of attempts in the past to solve this problem by mechanized or automated means. The starting point of the invention is a device of the type used specifically for the analysis of NPK fertilizers, which exist in the form of homogeneous dust-free granules. In this program controlled device, the sample which is furnished by the sampler in a discontinuous manner and only roughly defined with respect to its amount, is transferred to a funnel from whence a vibrator conveyor feeds the maaterial into a scale pan rotatable by 180.degree. around a horizontal axis, of a photomechanically controlled inclination balance. As soon as a predetermined amount of the sample has been accumulated in the scale pan, the vibrator conveyor is swung away, the scale pan is rotated by 180.degree. and the sample is tipped into a dissolving vessel in which a predetermined amount of solvent has previously been deposited from a solvent tank by means of an automatic pipette. The sample is dissolved therein; part of the solution is drawn off for the actual analysis; the remainder is discarded, and the dissolving vessel is rinsed, after which a new cycle may be started. In addition to the fact that this device is suitable only for samples which are absolutely dust free, have no tendency to stick and are largely homogeneous with respect to grain size, its design, its controls and its control programs are complicated, and it is therefore prone to malfunctions and/or disturbances.